I have been thinking about building a dolly just for the fun of it but I not very familiar with how you program/communicate with the motors which drive the dolly so that you can start and stop a timelapse. To be more specific, how does the motor in the dolly know when the camera is not taking an exposure? If I take an exposure on a dolly for 30 seconds, the dolly cannot move for 30 seconds until the exposure is complete, then the dolly must move a set distance before the next exposure begins. Am I going to have to program all of this or is there something that will help me slim down this procedure? Thanks guys.

You've got the procedure exactly. Trigger camera, wait until exposure is finished, move, wait, repeat. Some advanced controllers monitor the flash synch port to know when the shutter opens and closes, but most just do it with timing.

If you use timing to keep the dolly still while the shutter is open, consider having it move first, then wait, then shoot. There will be less conflict. My first controller used an external intervalometer which I already had for regular timelapse. When the intervalometer said go, it moved the motor, then triggered the camera after the move. As long as the interval was long enough, it worked great. More advanced units have their own intervalometer and have you enter an amount of time it should wait after triggering the shutter before it begins a move. A good controller will save this value so you don't have to enter it every time.

Dynamic still has some kits for making a copy of their MX-2 dolly controller. It can control two motors, and allows you to ramp up the speed going into the move and ramp down at the end if desired. It can do continuous movement if you want some motion blur for artistic reasons, and lots of other advanced features. If you don't mind soldering the components and downloading the software into an Arduino, its a bargain for $55. You'll probably spend more if you build your own from scratch. I just got one to assemble for a friend who is getting a dolly for Christmas. Last one I put together took about an hour or two. Here's a link to it in their online store.

Coding for a simple controller can be pretty easy. My first one used BCD thumbwheel switches because they served as both input device and display. There was no need to drive an LCD or have a menu system and buttons. I set the number of steps the motor should move on the thumbwheels. Whenever the intervalometer said go, it read the thumbwheels, moved that number of steps, then triggered the shutter. Direction was controlled by a toggle switch wired directly into the direction input on the motor driver.

Tue Dec 17, 2013 1:06 pm

calypsob

Joined: Fri Apr 06, 2012 7:29 pmPosts: 10

Re: Dolly for milky way timelapse

Man thats awesome thanks for the fast reply. Do you think I could control it via usb from a laptop instead of building a hardware device? the reason I ask is because I usually have everything out in the field with me when Im doing this sort of stuff, which means the telescope, deep cycle batt, mount, and cameras are all with me. So a laptop would be more convenient but not mandatory. Once I have this figured out my next objective is to mount an astrotrac or similar tracking platform to a panning dolly and see if the mount will remain polar aligned if I level out both ends of the panning platform. This will be interesting and I'm not sure if anyone has ever done this before.

If you want to use your laptop as a controller, just buy Dragonframe stop motion software. its very advanced. Some of the best shooters on this site use it for their motion control. You'll need an interface box that lets you plug your motors into and the box plugs into the USB. There is a sketch on the dragonframe website that turns an Arduino microcontroller into the required box if you are confident about wiring motor drivers to it. Its pretty easy with a little reading. Start at the Dragonframe site.

There are a few plug and play boxes for it if you don't want to build. Dragonframe sells a 16 channel box, but its expensive. The TB-3 pan-tilt head comes with a 3 channel dragonframe compatable controller built in, so it can control dolly, pan and tilt.

We will be selling an inexpensive Dragonframe box for about $100, but they won't ship in large numbers until sometime in the first half of next year. They are not on our website yet, but you can contact Frank through the site, and request one of the first ones. If he's not against it, there are a couple here you could possibly get if you're OK with the fact they don't have many hours of testing done yet. The site is

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